A Short Guide to Choosing a Physics List

Transcription

1 A Short Guide to Choosing a Physics List Geant4 Tutorial at Marshall Space Flight Center 19 April 2012 Dennis Wright (SLAC) Geant4 9.5

2 IntroducGon Which physics list you use is highly dependent on your use case Before choosing, or building your own, familiarize yourself with the major physics processes available the process- model catalog is useful for this see Geant4 web page under User Support, item 10b Geant4 provides several reference physics lists which are rougnely validated and updated with each release these should be considered only as stargng points which you may need to validate or modify for your applicagon There are also many physics lists in the examples which you can copy these are usually very specific to a given use case 2

3 IntroducGon There are currently 28 pre- packaged physics lists available but you will likely be interested in only a few, namely the reference physics lists many physics lists are either developmental or customized in some way, and so not very useful to new users All but one of the pre- packaged physics lists use templates the LBE physics list is the old- style flat list without templates or physics builders it is soon to be replaced with a more up- to- date flat list Reference physics lists: FTFP_BERT, QGSP_BERT, FTFP_BERT_HP, QGSP_BIC, Shielding plus a few more 3

4 Physics List Naming ConvenGon The following acronyms refer to various hadronic opgons QGS - > Quark Gluon String model (>~20 GeV) FTF - > FriGof string model (>~5 GeV) LHEP - > Low and High energy parameterized model (being phased out) BIC - > Binary Cascade (<~ 10 GeV) BERT - > BerGni- style cascade (<~ 10 GeV) HP - > High Precision neutron model ( < 20 MeV) P - > G4Precompund model used for de- excitagon EM opgons designated by no suffix : standard EM physics EMV suffix : older but faster EM processes 4

5 Reference Physics Lists FTFP_BERT recommended by Geant4 for HEP ATLAS plans to switch to this from QGSP_BERT contains all standard EM processes uses BerGni- style cascade for hadrons < 5 GeV uses FTF (FriGof) model for high energies ( > 4 GeV) QGSP_BERT all standard EM processes BerGni- style cascade up to 9.5 GeV QGS model for high energies (> 20 GeV) LEP (Low Energy Parameterized models) in between 5

6 Reference Physics Lists QGSP_BERT_EMV also recommended by Geant4 for HEP currently used by CMS same as QGSP_BERT, but with EM processes tuned for beger CPU performance increase in speed comes with a slight decrease in EM precision FTFP_BERT_HP same as FTFP_BERT, but with high precision neutron model used for neutrons below 20 MeV significantly slower the FTFP_BERT when full thermal cross secgons used there s an opgon to turn this off for radiagon protecgon and shielding applicagons 6

7 Reference Physics Lists QGSP_BIC same as QGSP_BERT but replaces BerGni cascade with Binary cascade and G4Precompound model recommended for use at energies below 200 MeV (many medical applicagons) QGSP_BIC_HP same as QGSP_BIC, but with high precision neutron model used for neutrons below 20 MeV recommended for radiagon protecgon, shielding and medical applicagons 7

8 Reference Physics Lists Shielding based on FTFP_BERT_HP with improved neutron cross secgons from JENDL beger ion interacgons using QMD model currently used by SuperCDMS dark mager search recommended for: shielding applicagons space physics HEP 8

9 Other Physics Lists (based on use case) If primary pargcle energy in your applicagon is < 5 GeV (for example, clinical proton beam of 150 MeV) start with a physics list which includes BIC or BERT e.g. QGSP_BIC, QGSP_BERT, FTFP_BERT, etc. If neutron transport is important start with physics list containing HP e.g. QGSP_BIC_HP, FTFP_BERT_HP, etc. If you re interested in Bragg curve physics use a physics list ending in EMV or EMX e.g. QGSP_BERT_EMV 9

10 Other Physics Lists (based on use case) For ion- ion physics lists see Tatsumi Koi (SLAC) a custom- designed physics list usually employs QMD model For opgcal photon transport start with the LBE physics list list is a bit old, but opgcal code can be extracted for other applicagons For radioacgve decay use LBE list as an example For detailed line emissions from EM processes LBE or see following slide 10

11 Alternate EM Physics Lists Up to now, most physics lists mengoned have used the standard EM processes, but low energy EM physics is also available G4EmLivermorePhysics (physics list suffix = LIV) G4EmLivermorePolarizedPhysics G4EmPenelopePhysics (suffix = PEN) G4EmDNAPhysics Physics lists containing these are recommended for micro- dosimetry applicagons For examples using a DNA physics list, go to geant4/source/examples/advanced 11

12 Using Alternate EM Physics Lists These physics list classes derive from the G4VPhysicsConstructor abstract base class A good implementagon example that uses these already available physics lists can be found in examples/extended/electromagnegc/testem2 Once you know the desired hadronic part of the physics list name (e.g. FTFP_BERT) an easy way to keep straight the various EM opgons is to use the G4PhysListFactory class: G4PhysListFactory factory; G4VModularPhysicsList* physlist = factory.getreferencephyslist( FTFP_BERT_ XXX ); // where XXX = EMV or EMX or LIV or PEN 12

13 Using Geant4 ValidaGon to Choose Physics Lists UlGmately you must choose a physics list based on how well its component processes and models perform physics performance CPU performance Geant4 provides validagon (comparison to data) for most of its physics codes validagon is a congnuing task, performed at least as oten as each release more validagon tests added as Gme goes on To access these comparisons, go to Geant4 website click on the Results and PublicaGons, then ValidaGon and tesgng, then Hadronic ValidaGon Web Pages then New ValidaGon Framework 13

14 New Hadronic ValidaGon Framework 14

15 IAEA ValidaGon Tests (Hadronic) 15

16 Specific Hadronic ValidaGon Test 16

17 DocumentaGon of Physics Lists When you run one of the reference physics lists, the log output will contain a list of processes and models included the energies over which they are applied similar informagon about cross secgon data sets will be included soon Geant4 web page will soon include html output of the above informagon 17